Field of the Invention
This disclosure relates to a developing unit that develops a latent image formed on an image carrier by an electro-photographic system, an electrostatic recording system, or the like to form a visible image.
Description of the Related Art
In an image forming apparatus using an electro-photographic system in the related art, an electrostatic latent image that is formed on an image bearing member, such as a photosensitive drum, is developed by a developing unit by using a toner. As such a developing unit, a developing unit adapting a vertical agitating and function separation type is known. This vertical agitating and function separation type developing unit is configured to array a first chamber for supplying a developer to a developing sleeve as a developer bearing member and a second chamber for collecting the developer from the developing sleeve vertically. In a case of a configuration disclosed in JP-A-5-333691, for example, a circulation path for circulating the developer between the first chamber and the second chamber is formed by partitioning the first chamber and the second chamber with a partitioning wall and causing a pair of communication portions formed in the partitioning wall to communicate between the first chamber and the second chamber.
Here, in the case of such a developing unit of the vertical agitating and function separation type as disclosed in JP-A-5-333691, an agent surface of the developer in the first chamber is inclined downward toward the communication portion for sending the developer from the first chamber to the second chamber. Then, a coating property of the developer easily becomes unstable, and for example, the developing sleeve is unevenly coated with the developer. Thus, it is considered that an apex of the partitioning wall positioned between the developing sleeve and a conveyor screw is lowered to facilitate the supply of the developer to the developing sleeve even at the position at which the agent surface is lowered.
However, in the case of the configuration of the vertical agitating and function separation type, a repelling pole for peeling off the developer from the developing sleeve in order to collect the developer from the developing sleeve to the second chamber tends to be arranged so as to be adjacent to the conveyor screw in a substantially horizontal direction. Therefore, if the apex of the partitioning wall is lowered as described above, an area where magnetic force becomes zero between the repelling poles tends to be positioned at or near a location where the developer is supplied from the first chamber to the developing sleeve. In such a case, the developer that is supplied from the first chamber to the developing sleeve tends to drop without being borne by the developing sleeve. If the developer drops as described above, the developer tends to be stored in the lower chamber that corresponds to the second chamber. Therefore, there is a possibility that dragging, in which the developer in the second chamber is dragged by the developing sleeve, occurs and the property of coating the developing sleeve with the developer becomes unstable. In addition, there is also a possibility that overflowing of the developer occurs because the developer on the developing sleeve cannot be sufficiently introduced into the second chamber.